My next steps are:
1. Install the I7500XXII5 firmware.
2. Try to install GALAXO ROM and see how it looks like
3. Try to install the MUTYMOD 2.0 ROM and test it
4. What is the build.prop file, and why do i need it?
5. On last thing, before i rooted my phone i did a factory reset (Before any change of my machine the factory reset is the same as i just bought this machine) But is see that i have lots of folder on my SD card from all previous reset applications, how can i remove them in a safe way? I want a clear SD card with the only files needed.
6. What does the clearapps.sh file?

Factory reset does not format SD card. Just remove everything from SD card manually. Only leave what you know you need. A casual user would normally have to keep the DCIM folder (your images and videos) and the media folder (your custom ringtones). You may also want to leave the nandroid folder, as it contains your backup.

You have not read the instructions carefully. clearapps.sh removes some applications to free up RAM.

Roll back is possible by either nandroid restore or by flashing stock firmware with Odin, the latter is preferable.

Sorry for my noob questions but what do you mean by "simply wipe your sd, re-flash"
1. How to wipe
2. How to reflash? Why do i need to reflash? Can't i just do a factory reset if I've installed the II5 ROM and want to go back to my ROM?

By wipe he meant the same as I meant - delete everything you don't need.
Ideally, copy everything you want to keep to your PC, format the internal SD card (from Phone Settings), then copy your stuff back.

Read the sticky threads for details on flashing. Factory reset only resets your user customizations, deletes installed programs - it reverts the firmware you flashed to it's pristine condition. It does not revert the phone to your original fw version.

Wiping your sd-card is done most easily by hooking the phone up to your pc with the usb-cable, and then deleting everything in the new drive that shows up (note: one of the two drives represents the removable sd-card and may not be mounted). I recommend doing this after doing a factory reset, this way you're sure to leave a blank phone.

Reflashing ... when you update the firmware to some other version (or a custom rom such as galaxo or mustymod), that's what a factory reset takes you back to. Nandroid will capture everything that's put on top of that (apps, settings, data), but does not include the firmware itself. Obviously, you can't use nandroid to restore to a state before nandroid was on the phone.

When you reflash with Odin, what you'll get is effectively a stock phone with the firmware you just flashed, with no extras such as nandroid.

You don't need nandroid. It's good for backing up your setup, but not absolutely necessary. If you decide to go back, you'll be starting from scratch. With nandroid, you can make a backup of your current setup, so when you return you can restore this and save yourself some grief.

An analogy:
- So you have XP on your pc, want to try Vista, but you want to be able to go back to XP in case you don't like it.
- You have the install files for Vista, so that's ready to go.
- Make sure you also have the install files for XP, or you won't be able to go back. Once you update, the old install is gone, see?
- Unfortunately, you can't easily copy out your existing XP install, you really do need the install files.
Makes sense?

Look into the stickies in this forum to get the latest stock firmware.

OK Now i'm consfused. Look at this thread: http://androidforums.com/samsung-i7500/11747-cellcom-israel-nandroid-backup-original-firmware.html
Shayko says: "i noticed a few people from israel who updated their firmware and wanted to return to the Cellcom original firmware and didn't know how or didn't have the original version to work with, so i made a clean Cellcom firmware nandroid backup which restores that firmware."
All he did is to backup with NANDROID and he says that if we use it we can go back to our original firmware, so who is right?

How did he managed to backup the firmware and then to go back to the original firmware

Thanks everyone, I have now android 2.0 on my Galaxy!!!
Amazing!!! Still missing some features like bluetooth but its great.
But I won't touch again any of Samsung Phones, after i will finish paying on my Galaxy (2 years from now) I'm sure i will have another android phone.

Seeing as we're getting the shaft from Samsung (even as far as 1.6 goes), I have a couple of questions for a new 2.0 user - did you Mustymod? Do you have - push gmail, full phone, full headset use, full 3g, full GPS, full wifi?
I'm like you, some 2 years left and I can't stick 1.5 for that long